1. Field of the Invention
The present invention relates to an FBT (fly-back transformer), its bleeder resistor (installed on the top of the FBT), and a device for coupling the bleeder resistor, the FBT being for generating a high voltage in cathode ray tube for use in television, monitor or the like. Particularly, the present invention relates to an FBT, its bleeder resistor, and a device for coupling the bleeder resistor, in which two or more openings are formed adjacently to a resistance pattern on a substrate, and the first and second openings are formed alternately and mutually facingly. Further, the sum total of the lengths of the first and second openings is made larger than the average distance between the first and second openings. Thus, when manufacturing the non-coated bleeder resistor, there are not needed the glass coating, the baking, the dipping into the epoxy resin, and the curing. Notwithstanding, the voltage resistant property is reinforced, and the manufacturing process is simplified. Thus the bleeder resistor can be manufactured in an easy manner with a decreased cost.
2. Description of the Prior Art
Generally, the conventional bleeder resistor is manufactured in the following manner. That is, as shown in FIG. 1, there is prepared a ceramic substrate 10 made of Al.sub.2 O.sub.3 having a purity of about 96%. Its thickness is about 0.5-1.2 mm, and its area is 400-1500 mm.sup.2. Upon the ceramic substrate 10, there is printed PbAg, PtAg, Ag or their combination paste. Then the printed substrate is baked at a temperature of about 800.degree. C., and thus, a printed circuit board is formed, and then lead wires are soldered. Then RuO.sub.2 is printed thereupon, and then the structure is baked at a temperature of about 850.degree. C. Thus a resistor having a certain thickness is completed.
Meanwhile, in this resistor, electric current can flow only if the electrical resistance per unit length of the resistor is smaller than the air contact electrical resistivity. In the case where the voltage breakdown resistivity of air is 0.5 KV/mm, if a voltage of 20 KV is supplied across a resistor 12, there has to be secured a distance of 20 KV.div.0.5 KV/mm=40 mm. Further, if the thermal degradation and the environmental factors are taken into account, then the safe distance must be 1.8 times as large as the above distance, that is, 40 mm.times.1.8=72 mm. Meanwhile, in the case where the resistor 12 is printed on the ceramic substrate 10 in a straight line, the length of the ceramic substrate has to be longer, with the result that the total bulk of the ceramic substrate becomes too large.
Therefore, the resistor 12 on the ceramic substrate 10 has to be made curved, so as to reduce the bulk of the ceramic substrate 10. In this case, however, the potential difference over per unit length of the curved pattern exceeds the straight line voltage breakdown resisting distance 0.5 KV/mm. If the environmental factors and the thermal degradation are taken into account, the potential difference per unit length far more exceeds the air voltage breakdown resisting distance, with the result that glow discharges may occur between the curved patterns. Therefore, conventionally after forming the curved resistor, the resistor patterns are insulated by a glass coating, and then, a sealed baking is carried out, thereby preventing the occurrence of the glow discharges.
Meanwhile, although the glass coating can insulate the patterns, the moisture and the thermal impact during the curing of the crystalline epoxy resin weakens the insulation, or damage the bleeder. Therefore, a dipping into the epoxy resin is carried out after the glass coating.
However, the bleeder resistor manufactured in the above method is accompanied by the following disadvantages.
First, the resistor 12 is printed upon the ceramic substrate 10, then a glass coating is carried out, then a baking is carried out, then the epoxy resin 15 is coated, and then its curing is carried out. Therefore, due to this complicated manufacturing process, the productivity is lowered, and the manufacturing cost rises.
Second, the resistor 12 is printed upon the ceramic substrate 10, then a glass coating is carried out to insulate the resistor patterns, then a baking is carried out, then the epoxy resin 15 is coated, and then its curing is carried out. Therefore, the characteristics of the printed resistor 12 are degraded, and the resistance error fluctuation rate is increased.
Third, due to the continued baking, the grains of the resistor are continuously rearranged, and therefore are easily deranged. Therefore, the surface of the resistor becomes rough and sharp, with the result that the resistance against the voltage breakdown steeply drops.
Fourth, the resistance error become higher as described above, and therefore, to cater to the consumers, incomplete products are discarded. Ultimately, the product price has to be decided higher.
Fifth, due to the use of glass and soft epoxy resin, the material cost is increased, with the ultimate result that the price is further increased.
FIGS. 2A-2E illustrate various examples of the conventional bleeder resistors. The total area of the ceramic substrate 10 on which the resistor is printed is dipped into the molten epoxy resin to coat the substrate. FIG. 2A illustrates a bleeder resistor having three lead lines 14, the lead lines being connected by soldering. Therefore, this resistor has the above described disadvantages. FIG. 2B illustrates a bleeder resistor in which the resistor patterns are formed very densely, and only one face of the ceramic substrate is coated.
FIG. 2C illustrates another conventional bleeder resistor in which only a part of one face of the ceramic substrate is coated with silicon. FIG. 2D illustrates a bleeder resistor in which a focus volume substrate is formed integrally, the resistor 12 is coated with an epoxy resin, and an opening is formed at a part of the substrate. FIG. 2E illustrates an example in which the focus volume substrate is integrally formed (it is not a bleeder resistor), and the straight distance between the openings (which are for insulating the patterns) is smaller than the width (W) of the ceramic substrate.
In the above described conventional techniques, there are the above described disadvantages due to the adoption of the glass coating and the soft epoxy coating. Besides, even if there are openings, glow discharges occur between the patterns all the same when the voltage rises to the rated level. Further, as described above, the complicated processes bring the lowering of the workability and the productivity.